Field of the Invention
The present invention relates to an air conditioning system, in particular for a motor vehicle.
Description of the Background Art
In motor vehicles, air conditioning systems are used for improving the comfort, in particular for providing a temperature that is pleasant for the driver. In a motor vehicle having an internal combustion engine, heating the interior of the motor vehicle is typically carried out via the engine's waste heat that is dissipated to a coolant circulating in a coolant circuit of the air conditioning system. In electric vehicles, which are operated by means of a battery, only little usable waste heat is generated at the electrical machine and the power electronics. Therefore, electrical auxiliary heaters are used, for example PTC (Positive Temperature Coefficient) heaters, which, however, consume additional electrical power, which, in turn, can result in a reduced range of the electric vehicle. For heating the interior of the motor vehicle, it is therefore an aim to provide a heat pump system for the air conditioning system present in the vehicle. The air conditioning system typically has a closed refrigerant circuit in which a refrigerant circulates, comprising a compressor, an evaporator, an expansion valve and at least one heat exchanger. The heat thereby released can be dissipated to a coolant which likewise circulates in a closed coolant circuit, and can be utilized for heating the interior of the vehicle. As an alternative, the heat thereby released can be dissipated to the air which flows through the heat exchanger and which can be fed into the interior of the vehicle.
When using an external heat exchanger which absorbs energy from the air and which can have surface temperatures below the freezing point, the moist air at the heat exchanger can freeze at outside temperatures around the freezing point. This can negatively influence the heat transfer and therefore the efficiency of heat transmission to the air. In addition, a flow path of the air can at least partially be blocked, in some cases be blocked even completely by a growing ice layer.
For this reason, the heat pump mode of air conditioning systems is provided with a deicing mode in which the frozen condensate can be thawed again. In this connection, switching between the deicing mode, which is also referred to as thawing mode, and a heating mode is normally known per se. In a first method, switching the process from a heating mode, in which icing can occur, to a deicing mode is provided. However, for the duration of the deicing mode, no heat can be extracted from the air. This reduces the overall efficiency of the heat pump. In a second method known per se, switching from the heating mode to the deicing mode takes place as well, but heat is extracted from a buffer storage. Here, the buffer storage contains a hot carrier medium which is fed through the cold external heat exchanger and can deice the latter in this manner. Such buffer storages are voluminous and result in additional weight of the motor vehicles.